Improved RF Power Performance of AlGaN/GaN HEMT Using by Ti/Au/Al/Ni/Au Shallow Trench Etching Ohmic Contact
Hao Lu, Xiaohua Ma, Bin Hou, Ling Yang, Meng Zhang, Mei Wu, Zeyan Si, Xinchuang Zhang, Xuerui Niu, Yue Hao
Abstract
In this article, we report on the high dc and RF performance of AlGaN/GaN high electron mobility transistors that employ Ti/Au/Al/Ni/Au metallization stack with shallow trench etching ohmic contact (STEOC). An excellent ohmic contact performance including low contact resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{C}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.28~\Omega \cdot $ </tex-math></inline-formula> mm and smooth surface morphology have been achieved simultaneously. Atomic force microscope (AFM) reveals a highly smooth surface morphology with a root mean square (rms) roughness of 6.3 nm even after 810 °C high-temperature annealing (HTA), achieving an improvement of 79% as compared to the conventional Ti/Al/Ni/Au ohmic contact (COC). A high-resolution transmission electron microscope (HRTEM) showed a glossy morphology with a continuous and uniform TiN layer formed in the interface for the STEOC sample, while a bumpy morphology caused from the Ni-Al complexes balling up and TiN island penetrating into the AlGaN/GaN heterostructure were observed for the conventional sample. Consequently, the fabricated transistors with the STEOC process show a high output current of 1.52 A/mm and low ON-resistance ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${R}_{ \mathrm{ ON}}$ </tex-math></inline-formula> ) of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.09~\Omega $ </tex-math></inline-formula> mm. In addition, a high current cutoff frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{T}$ </tex-math></inline-formula> ) of 60 GHz and maximum oscillation frequency ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}_{\text {max}}$ </tex-math></inline-formula> ) of 150 GHz were obtained for the STEOC HEMT with a gate length ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${L}_{\text {g}}$ </tex-math></inline-formula> ) of 150 nm. Sub-6 GHz continuous-wave mode power sweep measurements deliver a high power-added-efficiency (PAE) of 67%. These results show the significant potential of the STEOC process to facilitate the development of GaN-based power amplifier (PA) applied for 5G.